This invention relates to a supported acidic catalyst composition and various processes in which the catalyst can be employed to promote hydrocarbon conversion reactions especially useful in petroleum refining. More particularly, this invention is directed to a catalytic composition having superior stability in hydrocarbon conversions such as low temperature paraffin isomerization and paraffin alkylation, which comprises a fused salt complex of certain aluminum halides and manganous halides present on the surface of a porous, refractory carrier, and to its use in such hydrocarbon conversion processes.
Catalytic hydrocarbon conversion processes such as skeletal isomerization of isomerizable paraffins and cycloparaffins and ethylene alkylation of paraffinic hydrocarbons has long been recognized in the art. In the area of petroleum refining, processes such as paraffin isomerization have more recently acquired greater importance because of the need to maintain high octane ratings for motor fuels at the reduced levels of tetraethyllead or other organolead antiknock agents now mandated by environmental and legislative constraints. In this regard, isomerization of straight chain or slightly branched C.sub.5 and C.sub.6 paraffinic hydrocarbons to more highly branched hydrocarbons such as isopentane and dimethylbutane has been recognized as a viable alternative to the addition of lead compounds to motor fuel as a means of obtaining such high octane motor fuel.
The use of acidic hydrocarbon conversion catalysts of the Friedal-Crafts type in promoting isomerization and/or alkylation reactions is well known. In the case of paraffin or saturated aliphatic hydrocarbon isomerization, metal halides or mixtures of metal halides, e.g., aluminum chloride, aluminum bromide, zinc chloride, antimony chloride, etc., have generally been employed on a variety of refractory supports to effect isomerization of C.sub.4 to C.sub.6 hydrocarbons at temperatures ranging anywhere from 150.degree. to 600.degree. F., e.g., see U.S. Pat. Nos. 2,250,410 and 3,060,249. In such processes, a hydrogen halide is usually added along with the feed to act as a promoter or co-catalyst for the reaction while a hydrogen partial pressure is also maintained in the reaction zone to suppress undesired side reactions such as cracking of feed to lower molecular weight hydrocarbons and to prolong the catalyst life. To aid in suppressing these side reactions, it has been recognized that the catalyst composition, itself, can be modified via the incoporation of a hydrogenation component, e.g., platinum and platinum group metals, to impart a hydrogenation-dehydrogenation function along with the Friedal-Crafts activity, e.g., see U.S. Pat. Nos. 2,900,425, 2,924,629 and 2,999,074. Despite the numerous prior art disclosures dealing with such Friedal-Crafts catalysts, their acceptance on a commercial scale has not been outstanding in the area of paraffin isomerization. While the reasons for the limited commercial success of such catalyst are varied, some of the more substantial problems encountered include the requirement of higher reaction temperatures, e.g., 400.degree. F. or above, for adequate catalyst activity and the high rates of catalyst deactivation due to metal salt losses from the catalyst bulk and side reaction product, e.g., cracking, contamination of the catalyst. In the former case, higher isomerization reaction temperatures are undesirable because the formation of highly branched, high octane value-dimethylbutane is favored by low temperature, e.g., 200.degree. F., operation. In the latter case, metal salt losses, especially aluminum halides, via volatilization from the catalyst often require that additional halide be added to the reaction zone on a continuous basis and even then the catalyst lifetimes are not of sufficient duration to be attractive on a commercial scale. Accordingly, it would be of advantage if a Friedal-Crafts type catalyst could be developed which has good activity at low temperatures yet is not subject to deactivation to the extent previously encountered. In this respect it would be especially desirable if a catalyst composition employing aluminum halides as the acidic hydrocarbon conversion component could be found in which the need to continuously add fresh aluminum halide to the reaction zone is minimized or avoided since this addition significantly increases the costs and complexity of the process.